Rechargeable batteries, for example, nickel cadmium batteries, provide a renewable source of power for the increasing number of portable consumer and commercial electronic appliances. A problem related to the use of nickel cadmium (Nicad) batteries or cells is that newly manufactured cells are known to provide less than optimal performance than those cells which have been through a number of charge/discharge cycles.
Performance is measured by the number of ampere-hours one or more cells can provide at or above a useful output voltage. Thus, performance is not only a measure of the amount of energy that a cell delivers, but the manner in which the energy is delivered. A cell is more useful if it provides most of its energy at or above a useful threshold voltage instead of over a wide range of voltages. For example, a 1.2 volt cell that dissipates half of its stored energy at voltage levels below 0.8 volts is considered inefficient.
It is known that after several charge/discharge cycles, a Nicad cell will provide a better, in other words, a more square, voltage-time discharge curve. It has been found empirically that as many as 20 charge/discharge cycles may be required to obtain optimal performance. A consumer relying on such cells experiences inconvenience because of the shorter useful discharge time associated with newer cells.
One solution to the above described problem is to condition new cells by running the cells through approximately 20 charge/discharge cycles prior to their first use. This solution, however, is extremely wasteful with respect to time and energy.
Another disadvantage of Nicad batteries is that after a substantial number of charges, the ability of the battery to receive a satisfactory charge is inhibited. In U.S. Pat. No. 4,829,225, it is explained that this is due in part to the progressive accumulation of positive ions to the negative plate and negative ions to the positive plate. The accumulation of ions blocks further ions from reaching the plates, inhibiting charging. U.S. Pat. No. 4,829,225 ('225) further teaches that by charging the battery with a periodic signal that includes a short discharge cycle, the plates, and therefore the battery, may be reconditioned, thereby enabling the battery to receive a satisfactory charge. The periodic charging signal taught in '225 uses a periodic pulse of as high as 10 Hz, but preferably less than 2 Hz. In the embodiment disclosed therein, one pulse consists of 0.712 secs. and includes a 2 msec discharge pulse and a 10 msec stabilization period.